简答题All the vowel letters (a, e, i, o and u) can produce the central vowel sound /ə/.简答题The long vowel sound /i:/ and the short vowel sound /I/ only differ in vowel length.简答题To pronounce back vowels, speakers are supposed to raise the back of their tongue the highest.简答题All English vowels are voiced (浊音).简答题"Straight" and "street" share the diphthong /eɪ/.